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The scientific “unit” we call the decibel

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Re: The scientific “unit” we call the decibel

#271

Post by DonHopkins »

lambdaone wrote: post #187

It's a bit like hating numbers, and saying "What do you mean by 'three'; what is it - three volts, three amps, three metres? Clearly 'three' is meaningless, and we should stop using it and all the other numbers besides." decibels are simply a dimensionless ratio, used as a multiplier for some known value of some known quantity. In every context where decibels are used, either the unit they qualify is explicitly speci…

At least the Mel-frequency cepstrum is honest about being a perceptual scale anchored to human hearing, rather than posing as a universally-applicable physical unit.

https://en.wikipedia.org/wiki/Mel-frequency_cepstrum

>Mel-frequency cepstral coefficients (MFCCs) are coefficients that collectively make up an MFC. They are derived from a type of cepstral representation of the audio clip (a nonlinear "spectrum-of-a-spectrum"). The difference between the cepstrum and the mel-frequency cepstrum is that in the MFC, the frequency bands are equally spaced on the mel scale, which approximates the human auditory system's response more closely than the linearly-spaced frequency bands used in the normal spectrum. This frequency warping can allow for better representation of sound, for example, in audio compression that might potentially reduce the transmission bandwidth and the storage requirements of audio signals.

https://en.wikipedia.org/wiki/Psychoacoustics

>Psychoacoustics is the branch of psychophysics involving the scientific study of the perception of sound by the human auditory system. It is the branch of science studying the psychological responses associated with sound including noise, speech, and music. Psychoacoustics is an interdisciplinary field including psychology, acoustics, electronic engineering, physics, biology, physiology, and computer science.

Re: The scientific “unit” we call the decibel

#272

Post by nyeah »

regularjack wrote: post #241
skrebbel wrote: post #207

Earlier quoted context omitted.

To be frank, your comment just reads to me as a "stockholm syndrome" type reaction to a needlessly complex unit that you're intimately familiar with. You see the same in HN threads where people complain that eg Git or Rust are needlessly complex, there's a swath of people who are so emotionally invested in how well they understand the ins and outs of Git resp Rust that any suggestion that maybe things could be better…

There is no such thing as full volume, and there is not such thing as zero volume.

To be fair, since we can go to +3dB out of 0dB, we could also go to 200% on a 100% scale. In the era of software it would not be completely insane to allow users to choose how their faders are marked. (It would be insane to use 3/4 of a slider's travel for the range 100% to 400%. So the locations of the markings on usable sliders would remain mysterious to %-only folks.)

Ultimately people who use this a lot would choose to become familiar with dB, as they always have. But there's no rush.

Re: The scientific “unit” we call the decibel

#273

Post by hgomersall »

lxgr wrote: post #257
hgomersall wrote: post #249

Earlier quoted context omitted.

No, it always means a power ratio. That sometimes can imply something else, but that's on you to work that out.

Yes, but that, i.e. putting the burden of disambiguating some meaning from context on the receiver instead of the sender, is just bad communication.

What? Blaming a bad communicator for bad communication is fine. Blaming their words because they used them badly is not.

Re: The scientific “unit” we call the decibel

#274

Post by hgomersall »

lxgr wrote: post #254
hgomersall wrote: post #201

Earlier quoted context omitted.

It's a power ratio. 1dB always means a power ratio of 1.26. That might mean a voltage or current ratio, say, of 1.12, but that is because the relationship between voltage ratios and power ratios is a simple square.

That’s maybe what it “is”, but not the only thing people use it for in many fields. Very often, it’s a ratio between a measured quantity and some (implied) base unit of the same quantity.

In which case they're misusing it, which is hardly a problem with the notation.

Re: The scientific “unit” we call the decibel

#275

Post by DonHopkins »

regularjack wrote: post #241
skrebbel wrote: post #207

Earlier quoted context omitted.

To be frank, your comment just reads to me as a "stockholm syndrome" type reaction to a needlessly complex unit that you're intimately familiar with. You see the same in HN threads where people complain that eg Git or Rust are needlessly complex, there's a swath of people who are so emotionally invested in how well they understand the ins and outs of Git resp Rust that any suggestion that maybe things could be better…

There is no such thing as full volume, and there is not such thing as zero volume.

There such a thing as going to 11.

https://www.youtube.com/watch?v=uMSV4OteqBE

Re: The scientific “unit” we call the decibel

#276

Post by Aachen »

elfrinjo wrote: post #227

I'll summarize: It's annoying that dB is often used as a physical unit without the necessary suffix. It's annoying that the suffix seems quite random for most units It's annoying that the factor for power differs from the factor for voltage, etc. It's slightly annoying that it's usually decibel instead of Bel. However, we all agree that dBs are really useful.

> However, we all agree that dBs are really useful.

Which part of the article was that again? I was surprised to see that conclusion as summary because it's not what the takeaway seemed like to me, so went back to the article and I don't see this mentioned, perhaps I'm overlooking it because I didn't do a careful read a second time

Re: The scientific “unit” we call the decibel

#277

Post by formerly_proven »

viraptor wrote: post #243
klodolph wrote: post #234

Earlier quoted context omitted.

Sure, but the author is wrong. “How old is your son?” “He’s 3.” Clear in context. People write things like dB SPL (A-weighted) in spec sheets because spec sheets benefit from being unambiguous. Most of the time it’s really clear, like you’re talking about insertion loss or amplifier gain and there’s only one reasonable way to interpret it.

That only works if you're already familiar with the context and system and assume other people are too and don't care about anyone new to that area. (Good luck coming to the audio equipment datasheet with no experience and figuring out what the dB means in each case) "He's 3" works because of the previous question and because everyone had experience of talking about age. dB for anyone not already knowing the answer i…

Can you show one of those audio equipment datasheets where it just says " dB" a bunch of times and it's really unclear and confusing?

Re: The scientific “unit” we call the decibel

#278

Post by Aachen »

calmbonsai wrote: post #65

If you're specifying decibels in written form you always include the basis or you're simply being incomplete with your units. I don't understand the complaint there. In casual conversation, the context implies the basis. Dealing with decibels is also another shorthand to know the domain has a wide enough value gamut such that logarithmic values (where addition is multiplication) makes sense. See also, the Richter sca…

> If you're specifying decibels in written form you always include the basis or you're simply being incomplete with your units. I don't understand the complaint there.

It seems that a lot of people who are specifying decibels in written form aren't aware of what you just said

Did you ever see someone use p as a unit and expect anyone to understand it means pico? Because I've seen that with dB. In this very thread. You really don't have to look far for the tendency for dB to be used as incomplete unit

> See also, the Richter scale

Looking at the article and trying to substitute Richter, I can't imagine what you'd plug in the different positions:

- it's not a derivative of another relative unit (no decirichter)

- it was not originally meant for something else (dB was originally meant for power, leading to difference in meaning of dB in dB(V) vs. dB(W), if I'm understanding the article correctly)

- it's not trying to indicate the magnitude of the actual unit (you don't specify Richter-Volts or something, just Richter, so you can't forget to specify the actual unit)

- there aren't different meanings depending on the field you're in (a –45dB microphone is mentioned in the article as referring to Volts whereas an acoustic 10dB loudness difference is apparently in Pascals; Richters are always Richters)

The article criticises a lot of dB's aspects but I'm not sure the exponentialness is one of them

Re: The scientific “unit” we call the decibel

#279

Post by _kb »

skrebbel wrote: post #207
lambdaone wrote: post #187

It's a bit like hating numbers, and saying "What do you mean by 'three'; what is it - three volts, three amps, three metres? Clearly 'three' is meaningless, and we should stop using it and all the other numbers besides." decibels are simply a dimensionless ratio, used as a multiplier for some known value of some known quantity. In every context where decibels are used, either the unit they qualify is explicitly speci…

To be frank, your comment just reads to me as a "stockholm syndrome" type reaction to a needlessly complex unit that you're intimately familiar with. You see the same in HN threads where people complain that eg Git or Rust are needlessly complex, there's a swath of people who are so emotionally invested in how well they understand the ins and outs of Git resp Rust that any suggestion that maybe things could be better…

> volume sliders start at 0 dB and then go down to negative $MUCHO, until complete silence at -Infinity. And then this same unit is also used to measure how loud my coffee machine is.

They're not the same unit, at all.

The audio software is a skeuomorphism from an analogue mixing console that is applying a change to a signal. 0 is unity gain and deviation from this describes an amplitude variation. This is important, as it means you are either discarding information by lowering the level and reducing dynamic range, or interpolating new information (/ decreasing SNR) by applying gain. This is less important today with floating point, but has strong historical reasons for existence across both analogue and digital domains.

If you look at an audio power amp, you will likely have some form of positive number as this is applying gain. Depending on the context this may have some specific meaning or it may be a screen print of a Spinal Tap logo and the numbers 1..11. These are all just UI decisions and part of doing that well is presenting coherent information for the target user group.

When you're talking about an acoustic noise source this is dB SPL which is a quantifier against a physical reference. That reference level quantifier is omitted a lot, which leads us to a lot of the angst in this post and the comments here. These are precise measurements, with very specific meaning. Their expression is often sloppy, but the units aren't to blame.

(excuse me while I got "full HN" here - I appreciate the irony in this response noting your first few sentences)

The reason people respond strongly to comments like this (or those about Git, or Rust) is because details matter. When you immerse in a domain, you learn the reason for those details. That does not mean things can't be improved, but this also does not imply those details can be removed or are wrong. A lot of the world, particularly when working outside of the bounds of a computer, depends on necessary complexity.

Re: The scientific “unit” we call the decibel

#280

Post by jchw »

RichardLake wrote: post #255
klodolph wrote: post #234

Earlier quoted context omitted.

Sure, but the author is wrong. “How old is your son?” “He’s 3.” Clear in context. People write things like dB SPL (A-weighted) in spec sheets because spec sheets benefit from being unambiguous. Most of the time it’s really clear, like you’re talking about insertion loss or amplifier gain and there’s only one reasonable way to interpret it.

That depends, the dropped unit could be either a year or a month.

You don't drop the unit for months, so it's not ambiguous in context.
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